Dockerfile

FROM nginx:1.15.3-alpine
COPY site-template.conf /etc/nginx/conf.d/site.template
CMD sh -c "envsubst '\$SERVER_NAME \$ROOT \$PHP_BACKEND' < /etc/nginx/conf.d/site.template > /etc/nginx/conf.d/default.conf && nginx -g 'daemon off;'"

site-template.conf

server {
  listen 80;
  listen [::]:80;
  index index.html index.php;
  server_name ${SERVER_NAME};
  root ${ROOT};

  error_log /var/log/nginx/${SERVER_NAME}.error.log error;

  location / {
    try_files $uri $uri/ /index.php?$query_string;
  }

  location ~ \.php$ {
    fastcgi_pass ${PHP_BACKEND}:9000;
    fastcgi_split_path_info ^(.+\.php)(/.*)$;
    fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    fastcgi_param DOCUMENT_ROOT $realpath_root;
    fastcgi_intercept_errors off;
    fastcgi_hide_header X-Powered-By;

    fastcgi_buffer_size 128k;
    fastcgi_buffers 256 16k;
    fastcgi_busy_buffers_size 256k;
    fastcgi_temp_file_write_size 256k;

    include fastcgi_params;
    # Prevents URIs that include the front controller. This will 404:
    # http://domain.tld/index.php/some-path
    # Remove the internal directive to allow URIs like this
    internal;
  }
}